Figure 1. (a) A (14)--D-glucan molecule terminated by a ‘reducing end’ bearing a free (unsubstituted) hemiacetal hydroxyl (on the right) and a ‘nonreducing’ end (on the left). The hydroxymethyl groups at C6 of alternate glucose residues are on opposite sides of the chain. Each carbon atom of the glucose ring carries an axial hydrogen atom. For clarity, these are omitted.

Figure 2. Crystal structure of cellulose I. (a) Projection down the fibre axis (c) showing the layers (sheets) of cellulose chains hydrogen-bonded in the ac plane but lacking intersheet hydrogen bonding. The intersheet bonding involves van der Waals interactions between the hydrophobic faces of the glucose units. (b) View of a layer approximately perpendicular to the ac plane, showing the two intramolecular hydrogen bonds in the direction of the fibre axis (c) and the interchain hydrogen bonds. Reproduced from Kroon-Batenburg LMJ and Kroon J (1995) Carbohydrates in Europe 12: 15–19.

Figure 3. Schematic representation of the mode of packing in the unit cell of cellulose I. (a) Triclinic unit cell. (b) Monoclinic unit cell. The monoclinic angle is obtuse. Reproduced from Koyama M, Helbert W, Imai T, Sugiyama J and Henrissat B (1997) Proceedings of the National Academy of Sciences of the USA 94: 9091–9095.

Figure 4. Schematic diagram showing the differences between the monoclinic and triclinic forms of cellulose I. Each rectangle represents a single glucose unit, with a pair of glucose units (surrounded by a dotted box) constituting the cellobiose repeat due to the 2-fold screw symmetry along the chain axis (vertical in the diagram). In the monoclinic form, cellobiose units stagger with a shift of a quarter of the c-axis period (0.26 nm), whereas the triclinic form exhibits a diagonal shift of the same amount. The different spacings and angles shown depend on which crystallographic face is being viewed. Reproduced from Baker AA, Helbert W, Sugiyama J and Miles MJ (1997) Journal of Structural Biology 119: 129–138.

Figure 5. (a) Schematic representations of the cross-sections of typical cellulose microfibrils, ranging from Valonia cellulose to primary wall cellulose. Reproduced from Chanzy H (1990). In: Kennedy JF, Phillips GO and Williams PA (eds) Cellulose: Sources and Exploitation, Industrial Utilization, Biotechnology and Physicochemical Properties, pp. 3–12. New York: Ellis Horwood.

Figure 6. Atomic force microscope image of the surface of an acid-treated Valonia microfibril. The arrows at the top of the image point along the cellulose molecules, which are running almost vertically down the page. The dotted white box highlights an area where bright spots can be seen along the length of the molecules, separated by a distance closely matching the cellobiose repeat interval. The angle of the spots within the box to the molecular axis is 64±2°. Reproduced from Baker AA, Helbert W, Sugiyama J and Miles MJ (1997) Journal of Structural Biology 119: 129–138.

Figure 7. Microfibrils of G. xylinus cellulose associated with the surface of a bacterial cell. Cell surface showing the ribbon of cellulose growing thicker along the cell length as discrete bundles with separate points of origin (arrows) accumulate. Reproduced from Haigler CH and Benziman M (1982). In: Brown RM Jr (ed.) Cellulose and Other Natural Polymer Systems. Biogenesis, Structure and Degradation, pp. 273–297. New York: Plenum.

Figure 8. A fracture plane through the wall of an 18-day-old V. ventricosa cell showing regular but different orientations of the microfibrils in two lamellae. Reproduced from Itoh T and Brown RM Jr (1984) Planta 160: 372–381.

Figure 9. Microfibril orientation in the primary and secondary wall layers of a xylem fibre cell or a tracheid. On the inner surface of the primary wall layer (P), the microfibrils are arranged approximately transverse to the cell axis but are considerably disposed from this direction at the outer surface. In S₁, the outermost layer (next to the primary wall layer, P) the microfibrils are usually in a flat helix (relatively transverse), whereas in the S₂ layer they are in a steep helix (relatively longitudinal). The microfibrils in the S₃ layer are again in a flat helix (more transverse in orientation). Reproduced from Wardrop AB and Bland DE (1959) The process of lignification in woody plants. In: Kratzel K and Billek G (eds) Biochemistry of Wood, pp. 92–116. London: Pergamon Press.

Figure 10. Coiled microfibril bundles in the glomerulocytes in the epidermis beneath the test of the ascidian Metandrocarpa uedai. Reproduced from Kimura S and Itoh T (1995) Protoplasma 186: 24–33.